Here's my take. The ABG is a flawed concept from the beginning. The traditional double bass is just barely big enough to make low frequencies come out acoustically. The typical flat-top guitar isn't as loud as an arch-top guitar. Trying to make an ABG that really works as an acoustic instrument is going to require a very large body. In my experience the only two that ever had a chance of success were the original Guild B-50 and the Ernie Ball Earthwood. The only other thing that even came close was the Tacoma Thundercheif. I've never played the only other likely contender, the Taylor one.
All the others, including the Michael Kelly that I've played are so quiet that unless you're playing by yourself (or at most with a quite acoustic guitarist- maybe someone fingerpicking a Martin OM sized guitar) you're going to need an amp anyway. And most of them just don't sound very good amplified either. Add in the mechanical aspects, and if you're looking to buy a bass for your grandson to learn how to play bass, I think that for $300 you can get a much better instrument if you look at electrics.
John